Destroying Terrain

Most terrain features found on the battlescape can, with sufficient firepower, be destroyed. UFO outer hulls can be breached with a Blaster Bomb, inner UFO hulls can sometimes be breached by a Heavy Plasma, and weaker structures can be destroyed by more conventional weaponry, such as Grenades or sometimes even Rifles.

Being able to clear terrain in this manner is of great value. Aliens can lurk behind a wide variety of structures, ready to ambush you the second you enter their sight. Destroying terrain flushes the aliens out into the open, where they can be engaged far more safely. Entering rooms via breached walls is also usually far safer than coming in through an existing door — a common ambush point.

Damage vs. terrain

The general rule is that explosions will do a fixed 50% of their rated damage to a terrain feature, and projectile/beam weapons will do between 25% and 75% of their rated damage. The 50% damage for explosions is at the center of the explosion; damage will decrease by a constant amount the further away from the center you go. For more information on explosions in general, see Explosions.

If the damage dealt is equal or higher than the terrain's damage rating (or "armor"), the terrain will be damaged or even destroyed. If the damage is less than the terrain's damage rating, the terrain will be completely unharmed. See Explosions#Tile Characteristics for a table detailing several terrain types and their damage ratings.

UFO walls

The outer hull of a UFO has a damage rating of 100 points: as a result of this, only Blaster Bombs (Damage = 200) can breach them. Inner hulls and doors have a damage rating of 80 points. Heavy Plasmas, with a base damage of 115, can do between 28 and 86 points of damage to terrain. (86 - 79) = 7 values out of a range of (86 - 28) = 58 possible values (7 / 58) is 0.1206, which would mean Heavy Plasma shots will breach inner UFO walls 12.06% of the time. (Initial testing suggests this figure is must be correct: 250 Heavy Plasma shots breached 32 inner walls, for an average of 12.8%.) Expressed a different way, it should take an average of 8.29 Heavy Plasma shots to breach a UFO wall; three shots (one auto shot) have only a 32% chance of creating a breach. A full clip (35 shots) has a 1.11% chance of failing to break through.

Tank/Laser Cannon and Hovertank/Plasma both have a base damage of 110, which translates to a range of 27 to 82 against terrain objects. (3 / 55) is 0.0545, so these tanks should be able to breach inner UFO walls 5.45% of the time. It should take an average of 18.33 shots to breach a wall with either of these weapons.

The Hovertank/Launcher's fusion ball munition has an explosive damage of 140. 50% of 140 is 70, which means a Launcher tank can never breach inner UFO walls, although they can breach "vulnerable walls."

Security walls

Certain inner UFO walls and doors are more durable than the average inner wall. These so-called "security walls" have a damage rating of 100, like UFO outer walls, and can only be breached with the use of a Blaster Bomb. Security walls have a smooth, unsegmented appearance, with several bands running along the top. Security doors are darker than normal UFO doors and do not have a line running down their centers. The upper level of Battleships are constructed solely with security walls, although security doors are only used to enclose the central lift. See image below.

Vulnerable walls

A few wall types in UFOs are far easier to breach than normal inner walls. Most UFO navigation rooms (i.e., the bridge) have a few walls sporting a green and black computer display (see image above). These walls have a damage rating of 70 (versus 80 for normal inner walls) and can be more easily breached by a Heavy Plasma. They can even be breached by a direct hit from a Launcher tank's Fusion Ball.

Weaker still (60 damage) are the orange or blue flashing Alien Entertainment walls found in certain areas. The outer northern and western walls of alien base command centers are constructed of these walls (see image below), and are easy to breach — making for a safer entry point than the doors on the western face. Furthermore, on the northern side of the inner wall, there is a single computer panel wall which is easy to breach (all the other sections are "security walls" and can only be breached by a Blaster Bomb).

UFO floors

Like walls, floor tiles can be breached. Normal metal UFO floors have a damage rating of 80, but cannot be bypassed until they are fully destroyed. This requires two shots at a minimum: one to damage the floor, and another to destroy it. A damaged UFO floor has a damage rating of only 50, so it is not terribly hard to fully breach a UFO floor.

Breaching floors is useful in much the same way as breaching walls is: it allows your soldiers an alternative and often safer entry point into a room which may contain several aliens. Floors both above and below your soldiers can be breached. To shoot the floor above you (in essence, the ceiling), you must aim at a point on the level above you.
To shoot at the floor of your current level, just shoot at a square not bordered by any walls (or else the walls will be shot at instead of the floor). Naturally, soldiers in Flying Suits are needed to take fullest advantage of a hole in the ceiling.

Shooting through the ceiling may be of greatest use when storming an alien base command center. The command center's purple floors are weaker than the metal variety (50 intact/65 damaged — Heavy Plasma works well), and if you pick the right location, you can come up hidden behind an object. You may also be able to see and attack aliens on the upper floor once the ceiling is shot out, which is a much less risky approach than taking the lift up blindly into their midst.

Breaching walls and line of sight

If you shoot through a wall (or ceiling) and find yourself facing an alien, the alien will often return fire as soon as it sees you. To minimize this danger, it is best to shoot at walls from an oblique angle, keeping the shooter out of the aliens' line of sight. Return fire will only be directed at the shooter (if visible); other units standing in front of the breach will not be fired upon until they act, allowing you to get in the first shot at any aliens you discover on the other side.

Cydonia structures

Weapon damage ranges

Projectile/energy weapons

These are the damage ranges of these weapons vs. terrain objects (0.25 to 0.75 their normal rated damage). Their damage range vs. living creatures is between zero and twice rated damage.

Pistol

6.5 - 19.5

Rifle

7.5 - 22.5

Autocannon-AP

10.5 - 31.5

Laser Pistol

11.5 - 34.5

Plasma Pistol

13 - 39

Heavy Cannon-AP

14 - 42

Laser Rifle

15 - 45

HWP Cannon

15 - 45

Plasma Rifle

20 - 60

Heavy Laser

21.25 - 63.75

HWP Laser or Plasma

27.5 - 82.5

Heavy Plasma

28.75 - 86.25

Explosive weapons

Damage listed is for center of explosion, decreasing with distance. Damage range vs. living creatures is between one to three times these values.

Autocannon-HE

22

Grenade

25

Heavy Cannon-HE

26

Proximity Grenade

35

Small Rocket

37.5

HWP Rocket

42.5

Alien Grenade

45

Large Rocket

50

High Explosive

55

HWP Fusion Bomb

70

Blaster Bomb

100

Built-in alien weapons

These are the damage ranges of these weapons vs. terrain objects (0.25 to 0.75 their normal rated damage). Their damage range vs. living creatures is between zero and twice rated damage.

Note that the damage range of Celatids' attack is great enough that it can penetrate a UFO outer hull 7.14% of the time. However, due to the grenade-style aiming of the attack, it cannot be aimed directly at walls — just squares. In practice, diagonal and "rear" UFO walls can sometimes be targeted, especially on the second floor (see Explosions#When Is a Wall not a Wall). UFO roofs can also be targeted.

Cyberdiscs can penetrate UFO inner walls approximately 27% of the time.